The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Cardiovascular diseases are the most common cause of death worldwide. Currently, there are no effective portable and low-powered devices or systems that can be used for the non-invasive continuous monitoring of the cardiovascular system. The monitoring and treatment of medical and surgical conditions such as sepsis, congestive heart failure, hypertension, trauma, and other acute and chronic diseases could tremendously benefit from devices that allow direct or indirect continuous monitoring of important cardiovascular parameters in a nonintrusive manner. For example, monitoring cardiovascular parameters such as blood pressure waveform analysis (BPWA) and derivatives such as pulse pressure variability (PPV), or heart rate complexity changes such as heart rate variability (HRV) or respiratory rate (RR), or event dynamic changes in arterial vessel wall stiffness and the like could lead to effective measures for analyzing physiological conditions. That's because, at least in part, features extracted from these cardiovascular parameters have been shown to be highly correlative with a number of physiological conditions. Therefore, an effective technique for monitoring could provide caregivers with a variety of valuable clinical decision-making tools.
Yet, current techniques for continuous blood pressure (BP) and blood pressure waveform measurement are problematic. The techniques are invasive and confined to stationary complex clinical settings such as the intensive care unit (ICU). Hence, the techniques are not suitable for a wide range of applications, including personal healthcare monitoring.
Non-continuous monitoring systems have been proposed, but these too are problematic. Some of these non-continuous monitoring systems are relatively portable and non-invasive. However, they fail to provide the true waveform data of blood pressure and vascular tone (i.e., the degree of constriction experienced by a blood vessel relative to its maximally dilated state). Instead, these conventional techniques, whether from limitations in sensor sensitivity or limitations in data analysis, produce a reduced waveform data. They are incapable of producing true waveforms resulting from vascular wall movement or motion that are reflective of vascular tone, which are, as we show with the novel techniques described below, highly informative and rich with extracted clinically-useful information. Moreover, the majority of current noninvasive systems are cumbersome, since inflation of their mechanical cuff (or balloon) obstructs the normal everyday activities of life for the users. The systems are not usually wearable; and the information they provide lacks the frequency and granularity in which to take advantage of advances in the fields of signal processing and artificial intelligence. Further still, conventional noninvasive systems have been demonstrated to become inaccurate when patient physiology is labile, as occurs in critical states like hemorrhage or sepsis.
In light of these limitations and given the increased need for health care delivery models, there is a strong need to develop low-cost wearable monitoring systems that can span from the home to the hospital and that are capable of providing deeper physiologic information that help both health care providers and patients manage disease states in a more real-time fashion.